Turbocharged engines of the type used, for example, in off-highway and on-highway trucks, often employ wastegate valves for controlling the turbocharger speed and thus the boost air pressure delivered to the intake manifold of the engine. The wastegate valve is normally disposed in the exhaust system of the engine and controls the speed of the turbocharger by modifying the volume of exhaust gasses directed to the turbine section of the turbocharger. Typically, the wastegate valve may be pneumatically actuated based on boost air pressure. Boost air pressure is directly supplied from the turbocharger compressor outlet, charge ducts, or intake manifold to the wastegate valve. As boost air pressure increases, its force gradually acts against an energy storage device configured to urge the wastegate valve closed, thereby variably opening the wastegate valve based on air pressure.
Alternatively, turbocharged engines employ engine oil instead of boost air pressure to actuate wastegate valves. A control system employing engine oil for actuating a wastegate valve is described in U.S. Pat. No. 5,079,921 (the '921 patent) to McCandless et al., issued on Jan. 14, 1992. The '921 patent describes an exhaust back pressure control system for an internal combustion engine, in particular, a diesel engine, to improve engine warm up upon starting in a cold environment. The control system includes a valve assembly mounted at a turbine discharge outlet of a turbocharger. The position of the valve assembly is controlled by a microcomputer through an electrically controlled hydraulic valve using engine lubricating oil pressure to provide a controlled increase of exhaust back pressure on the engine during cold start up periods, thereby decreasing the warm-up period for the engine. The valve is selectively operated based on a signal from the microcomputer, the signal being calculated from various engine parameters, such as, coolant temperature, ambient temperature, engine speed, engine load, and time since engine start.
Although the control system of the '921 patent may variably actuate a wastegate valve in response to various engine parameters by employing a fluid other than boost air pressure, it may have limitations. For example, the control system of the '921 patent may not account for variations in boost air pressure that may be necessary in connection with a variable valve actuation system. The control system of the '921 patent may not satisfactorily provide wastegate valve control in response to variable valve actuation parameters in an internal combustion engine employing a variable valve actuation system.
The hydraulically operated wastegate valve control system of the present disclosure is directed towards improvements to the existing technology.